What is a Roller-cam Brake?

A roller-cam brake works like a centerpullcaliper, but its pivots are attached directly to the frame or fork. Instead of having a transverse cable, a roller-cam brake uses a triangular cam. The brake has two see-saw like arms, pivoted in the middle on studs. The cam is pulled by the cable, which is attached to the narrow end of the triangular piece. As the cam is pulled, its sloping sides push outward on rollers which are attached to the upper end of the brake arms. Roller-cam brakes permit the use of variable ratios by making the sides of the cam curve instead of being straight. Typically this is done to make the shoes travel in toward the rim fast, then more slowly as they engage...this gives more mechanical advantage in the actual braking range of travel, while allowing the shoes to back off farther from the rim than if the mechanical advantage were consistent throughout the travel range.

Compared to traditional cantilever brakes, roller-cams have the advantage of not protruding past the sides of the frame, which made them popular in the late '80's when there was a fad for placing the rear brake under the chainstays...you couldn't use conventional cantilevers there, because the cranks would bump into them.

Unfortunately, roller-cams are more difficult to set up than conventional cantilevers, and they make for more-difficult wheel changes.

Roller-cam brakes do not work on cantilever studs made for conventional cantilevers, because conventional cantilever studs are mounted inward from the rim, while roller-cam studs are outward from the rim. "U-brakes" are interchangeable with roller-cams.

With both roller-cams and U-brakes, there is a tendency for the brake shoes to strike higher and higher on the rim as the pads wear. If the pads are not checked regularly, they eventually start to rub on the sidewall of the tire, destroying the tire in short order.

Roller-cam brakes were developed by Charlie Cunningham, one of the Marin County, California mountain-bike pioneer bicycle builders. Roller-cam brakes were first sold by Wilderness Trail bikes, and were made in quantity by SunTour.

Cunningham has continued to refine his brake designs with "toggle link" and "lever link" versions replacing the cam and rollers, using the same brake arm and pivot locations.

The Odyssey "Pitbull" is a caliper-type roller-cam unit, popular in BMX and recumbent applications.

Check the brake shoe adjustment frequently due to their migrating higher and higher up on the rims. If you don't keep on top of the adjustment, the brake shoes will eventually start rubbing on the tire sidewall. Many thousands of tires have been ruined by this. Also, as the shoes wear, the transition point from low to high mechanical advantage gets farther from the rim, and eventually the cam may run out of travel, and so the brake shoe travel also must be adjusted..